An elastic wave road detection apparatus

Abstract

This application discloses a road inspection equipment based on elastic waves, relating to the field of road inspection. It includes: a data control system for controlling the excitation of a seismic source system, acquiring and recording simulated seismic signals received by a geophone system and the spatial coordinate data of the geophone system; a geophone system comprising multiple gravity-coupled geophones spaced at intervals along the circumference of a wheeled frame, for receiving simulated seismic signals generated by the seismic source system and coupled to the ground, converting the simulated seismic signals into electrical signals and transmitting them to the data control system; a seismic source system, under the control of the data control system, generating simulated seismic signals and coupling them to the ground; and a wheeled frame for mounting the geophone system and the seismic source system, driving the seismic source system and the geophone system to acquire data on the structure beneath the road during movement. Addressing the low efficiency of deep road defect detection in existing technologies, this application improves the efficiency of deep road inspection.

Description

Technical Field

[0001] This application relates to the field of road inspection, and in particular to a road inspection equipment based on elastic waves. Background Technology

[0002] As a crucial infrastructure of the modern transportation system, the construction quality and performance of roads are vital to the healthy development of society and the economy. However, due to the combined effects of vehicle loads and environmental factors over long periods, roads inevitably develop internal defects such as cracks, voids, and loosening. If these defects are not detected and repaired in a timely manner, they will lead to pavement damage, shorten the road's service life, and even cause safety accidents, resulting in serious economic losses and social impacts.

[0003] In recent years, with the rapid development of electronic information and sensor detection technologies, non-destructive testing methods for road defects have made significant progress. Ground-penetrating radar, high-frequency surface wave detectors, and digital imaging equipment have emerged, improving the accuracy and speed of defect identification to some extent. However, their detection depth is limited, making it difficult to obtain information about deeper defects.

[0004] In related technologies, such as Chinese patent document CN109001794A, a vehicle-mounted mobile seismic detection system suitable for urban environments is provided. This system includes at least one mobile vehicle-mounted seismic source subsystem and at least one mobile vehicle-mounted observation subsystem. The mobile vehicle-mounted seismic source subsystem includes a first vehicle body, and a seismic source, a seismic source control module, a seismic excitation recording module, a positioning module, and a seismic excitation-observation synchronization control module mounted on the first vehicle body. The seismic source control module controls the seismic source to strike the ground and generate seismic waves, and the seismic excitation recording module records the spectrum and waveform curve of the generated seismic waves in real time. The mobile vehicle-mounted observation subsystem includes a second vehicle body, and an observation data acquisition module, an observation control module, a recording and storage module, a positioning module, and a seismic excitation-observation synchronization control module mounted on the second vehicle body. The observation control module controls the observation data acquisition module to acquire seismic wave signals, and the recording and storage module stores the acquired data. The positioning module detects the position of its vehicle body, and the seismic excitation-observation synchronization control module controls the synchronization of the seismic excitation of the first vehicle body and the observation and data acquisition of the second vehicle body via wireless signal transmission. However, in this scheme, the seismic source subsystem and the observation subsystem are each mounted on different vehicle bodies and synchronized via wireless signals. This design may limit the system's efficiency in detecting deep road defects because it is necessary to ensure the synchronization of the seismic source and observation data. In urban environments, especially under complex road conditions, this synchronization may be reduced by vehicle movement and environmental changes. Summary of the Invention

[0005] To address the problem of low detection efficiency of deep road defects in existing technologies, this application provides a road detection equipment based on elastic waves, which improves the detection efficiency of deep roads by employing gravity-coupled contact source excitation and detection technology, temperature-compensated energy adaptive control, etc.

[0006] The purpose of this application is achieved through the following technical solution.

[0007] This specification provides a road detection equipment based on elastic waves, comprising: a data control system, a geophone system, a seismic source system, and a wheeled frame; the data control system is used to control the excitation of the seismic source system, acquire and record the simulated seismic signals received by the geophone system and the spatial coordinate data of the geophone system; the geophone system includes multiple gravity-coupled geophones spaced at intervals along the circumference of the wheeled frame, used to receive the simulated seismic signals generated by the seismic source system and coupled to the ground, and convert the simulated seismic signals into electrical signals and transmit them to the data control system; the seismic source system, under the control of the data control system, generates simulated seismic signals and couples the simulated seismic signals to the ground; the wheeled frame is used to mount the geophone system and the seismic source system, and to drive the seismic source system and the geophone system to acquire data on the structure beneath the road during movement.

[0008] The wheeled frame comprises a wheeled support frame and multiple wheels rotatably connected to the wheeled support frame. The wheeled support frame is used to mount the detector system and the seismic source system, and the multiple wheels are used to move the wheeled support frame on the road. The wheeled frame houses a battery pack, which is electrically connected to the seismic source system and the data acquisition and control system via wires, providing power to these systems.

[0009] In road inspection, excitation refers to the process of artificially applying mechanical force to generate elastic stress waves on the road surface. Common excitation methods include drop hammers, oscillators, and ultrasonic transducers. The stress waves generated by excitation propagate within the road, carrying information about the physical properties of the medium. By analyzing the propagation characteristics of the stress waves, road structural parameters can be determined. Excitation is a prerequisite for non-destructive testing of roads, and its quality directly affects the signal-to-noise ratio and resolution of the system. A gravity-coupled geophone is a sensor that converts ground vibrations into electrical signals. Its sensitive elements are typically piezoelectric crystals, capacitive diaphragms, or velocity sensing coils, and it can operate within a vibration acceleration range of 1 mG to 1 G. "Gravity coupling" refers to the way the geophone is coupled to the ground, utilizing the geophone's own weight to generate a normal pressure with the ground, synchronizing their vibrations. Compared to fluid-injection coupling, gravity coupling does not require a lubricating medium, making it suitable for continuous vehicle-mounted operation, but it carries a certain risk of decoupling. Data on the subsurface structure refers to digital quantities reflecting the physical properties of hidden targets such as the roadbed, pavement, and pipelines. Specifically, this includes: roadbed compaction, pavement thickness, void distribution, and pipeline burial depth. These data, obtained through the inversion of seismic signals, serve as the basis for evaluating road conditions and guiding maintenance. Due to the complexity of road structures, obtaining comprehensive and accurate subsurface structural data is a complex systems engineering project that requires coordination from excitation and detection to signal analysis.

[0010] Furthermore, the data control system includes: a trigger switch, a GPS positioning system, an amplifier circuit, and a control circuit; the trigger switch is used to generate a high-level trigger signal to trigger the source system excitation and data acquisition, and transmits the high-level trigger signal to the source system and the control circuit; the GPS positioning system is used to acquire the spatial coordinate data of the gravity coupling detector, and transmits the acquired spatial coordinate data to the control circuit; the amplifier circuit is used to amplify the simulated seismic signal acquired by the gravity coupling detector, and transmits the amplified seismic signal to the control circuit; the control circuit, upon receiving the high-level trigger signal, acquires the spatial coordinate data and the amplified simulated seismic signal and correlates them to obtain seismic waveform data with spatial coordinates.

[0011] The high-level trigger signal is a square wave signal with a relatively high amplitude (e.g., 5V) and a short duration (e.g., 10µs), commonly used for synchronization and timing in control systems. In road detection, the high-level trigger signal is generated by the control circuit and sent to both the seismic source system and the data acquisition system, instructing them to work synchronously. When the seismic source system receives the trigger signal, it immediately initiates the excitation process; after receiving the trigger signal, the data system begins recording the detector data until the trigger signal disappears. The accuracy and real-time performance of the trigger signal determine the alignment of the seismic source and detector data.

[0012] The trigger switch includes an elastic element and a contact. One end of the elastic element is fixedly connected to one end of the contact, and the other end of the elastic element is fixedly connected to the housing of the trigger switch. When the trigger switch contacts the ground and is subjected to a preset threshold pressure, the elastic element deforms, pushing the other end of the contact to make contact with the other contact of the trigger switch, causing the trigger switch to close and generate a high-level trigger signal. The GPS positioning system includes a GPS antenna and a GPS receiver. The GPS antenna is mounted on the top of the wheeled frame to receive GPS satellite signals; the GPS receiver is mounted on the wheeled support frame to decode the GPS satellite signals received by the GPS antenna and obtain spatial coordinate data.

[0013] Furthermore, the amplification circuit amplifies the simulated seismic signal, including: converting the acquired simulated seismic signal into an electrical signal and transmitting it to the amplification circuit; rectifying and filtering the electrical signal to obtain a DC signal reflecting the amplitude change of the electrical signal; comparing the DC signal with a preset amplitude threshold voltage to determine whether the current electrical signal amplitude is within a preset signal dynamic range, and obtaining an electrical signal amplitude detection result; amplifying the electrical signal according to a preset amplification factor control strategy based on the electrical signal amplitude detection result; and converting the amplified electrical signal into a digital signal as the amplified simulated seismic signal.

[0014] Rectification and filtering is a signal processing method that converts AC signals into DC signals, commonly used for envelope extraction and amplitude detection. "Rectification" refers to using nonlinear devices such as diodes to unidirectionally conduct the AC signal, causing the amplitude of one half-cycle to become zero, resulting in pulsating DC. "Filtering" refers to using passive networks such as RC and LC networks to smooth the rectified signal, removing high-frequency pulsating components and obtaining a stable DC level. Rectification and filtering can convert the amplitude information of analog seismic signals into easily processed digital quantities, providing a basis for signal amplification and threshold determination.

[0015] Preferably, the electrical signal undergoes multi-stage amplification and adaptive filtering to obtain an amplified and filtered electrical signal. The multi-stage amplification and adaptive filtering process includes: passing the electrical signal sequentially through a pre-amplification circuit, a bandpass filter, and a main amplification circuit for multi-stage amplification; the pre-amplification circuit uses a low-noise amplifier, and the main amplification circuit uses a variable gain amplifier; inputting the multi-stage amplified electrical signal to an adaptive notch filter; the adaptive notch filter automatically adjusts its center frequency, bandwidth, and notch depth parameters based on the main interference frequency components in the electrical signal to perform adaptive notch filtering, effectively suppressing power frequency interference and harmonic interference; amplitude detection is performed on the amplified and filtered electrical signal to obtain its amplitude value; the amplitude detection circuit uses a true RMS detector, which performs full-wave rectification and low-pass filtering on the electrical signal to obtain a DC signal proportional to the electrical signal amplitude, and then converts the DC signal into a digital signal for output; a combination of multi-stage amplification and adaptive filtering is used to amplify and suppress interference in weak seismic signals. By inserting bandpass filters between different amplification stages, noise and interference in the amplifier circuit can be effectively reduced. Introducing an adaptive notch filter to perform adaptive notch filtering on the amplified electrical signal can automatically adjust the filter parameters according to the actual interference situation, achieving accurate filtering of major interference frequencies such as power frequency interference and improving the signal-to-noise ratio of the signal.

[0016] Furthermore, based on the electrical signal amplitude detection results, the electrical signal is amplified according to a preset amplification factor control strategy. This includes: setting multiple preset signal amplitude thresholds, which divide the signal into different amplitude ranges; comparing the current electrical signal amplitude with each amplitude threshold to determine the amplitude range to which the current electrical signal belongs, and selecting the amplification factor corresponding to the amplitude range from the preset amplification factor control strategy; amplifying the electrical signal using the selected amplification factor; determining whether the amplitude of the amplified electrical signal exceeds a preset upper limit threshold for signal amplitude; if it exceeds the upper limit threshold, reducing the value of the selected amplification factor and using the reduced amplification factor to amplify the electrical signal until the amplitude of the amplified electrical signal is less than the preset upper limit threshold for signal amplitude, thus obtaining an amplitude-limited amplified electrical signal, which is then used as the amplified electrical signal.

[0017] In this process, when amplifying the electrical signal, the amplitude range of the signal is first determined based on the amplitude detection results. Then, the amplification factor corresponding to that range is selected from a preset amplification factor control strategy, and a variable gain amplifier is used to amplify the signal by the specified factor. This allows different amplification factors to be used for electrical signals with different amplitude ranges, avoiding signal distortion caused by excessive amplification or low signal-to-noise ratio caused by insufficient amplification. Simultaneously, to prevent the amplified signal amplitude from exceeding the system's dynamic range, an upper limit threshold for signal amplitude is introduced. When the amplitude of the amplified signal exceeds this threshold, the gain value of the variable gain amplifier is decreased to limit the signal amplitude within a reasonable range, preventing signal distortion and improving the adaptability of the amplifier circuit.

[0018] Preferably, a multi-stage amplification structure is adopted, dividing the amplification process into multiple steps such as pre-amplification, main amplification, and post-amplification. The pre-amplification uses a low-noise amplifier (LNA) to improve the signal-to-noise ratio of weak signals; the main amplification uses a variable gain amplifier (VGA), which adjusts the gain according to the AGC control voltage to achieve adaptive adjustment of the signal amplitude; the post-amplification uses a limiting amplifier (LA) to clip and limit the signal, preventing signal overload. This multi-stage amplification structure can fully utilize the advantages of various amplifiers, reducing noise while expanding the dynamic range of the signal.

[0019] Preferably, predistortion compensation technology is employed to preprocess the amplifier's input signal and counteract the amplifier's nonlinear effects. Commonly used predistortion compensation methods include lookup table method and function fitting method. The lookup table method establishes a compensation value lookup table by testing the amplifier's input and output characteristics. The corresponding compensation value is retrieved from the table based on the input signal amplitude and superimposed on the input signal to achieve inverse compensation for nonlinear distortion. The function fitting method uses mathematical modeling to fit the amplifier's nonlinear transfer function, then calculates its inverse function, preprocesses the input signal, and thus cancels out distortion. Predistortion compensation can effectively improve the amplifier's linearity and increase the signal's dynamic range and signal-to-noise ratio.

[0020] Furthermore, the gravity-coupled detector includes: a gravity-coupled contact-type source transducer, a source excitation control module, and a high-voltage power supply; the source excitation control module is used to receive a high-level trigger signal from a trigger switch and generate a first digital control signal and a second digital control signal according to preset excitation parameters; the first digital control signal is used to indicate the number and frequency of source excitation and is input to the frequency control interface of the high-voltage power supply by the source excitation control module; the second digital control signal is used to indicate the temperature compensation value of the high-voltage pulse peak voltage and is input to the amplitude control interface of the high-voltage power supply by the source excitation control module after digital-to-analog conversion. A high-voltage power supply, based on the first digital control signal obtained from the frequency control interface, supplies power to the gravity-coupled contact source transducer via a high-voltage switch according to the indicated frequency and number of cycles. The high-voltage power supply also adjusts the peak voltage of the high-voltage pulse signal output to the gravity-coupled contact source transducer based on the analog control voltage obtained from the amplitude control interface. The gravity-coupled contact source transducer uses a piezoelectric ceramic stack as the excitation element, generating mechanical vibration under the excitation of the high-voltage pulse signal. This mechanical vibration is transmitted to the base plate via a vibration transmission rod, generating a simulated seismic signal, which is then coupled to the ground. The source excitation control process is divided into two parts: frequency control and peak voltage control. Frequency control is directly implemented using digital control signals, while voltage control uses analog control voltage regulation, simplifying the control process. An ambient temperature sensor is introduced to compensate for peak voltage changes based on temperature variations, ensuring a constant excitation energy.

[0021] Among them, the gravity-coupled contact-type seismic source transducer is a device that utilizes the inverse piezoelectric effect of piezoelectric materials to convert electrical energy into mechanical vibration energy. Its main components include a piezoelectric ceramic stack, a top hammer, a base plate, and damping springs. When a pulsed voltage is applied to the piezoelectric ceramic, the ceramic undergoes axial deformation, propelling the top hammer to fall at high speed, impacting the base plate and generating a mechanical shock wave. The base plate contacts the ground, coupling the shock wave into the ground to form an elastic stress wave. "Gravity coupling" means that the transducer maintains contact with the ground by its own weight, without the need for other coupling devices. This type of transducer has a compact structure, high excitation efficiency, and is suitable for continuous operation on mobile platforms. The high-voltage power supply is a power device that converts low-voltage DC power into high-voltage pulsed power. Its core components are a step-up transformer and a power switching transistor. The primary winding of the step-up transformer is connected to the low-voltage DC bus, and the secondary winding is connected in parallel with a large capacitor and the seismic source transducer. When the switching transistor is turned on, the primary winding stores energy, and a high voltage is induced in the secondary winding. When the switching transistor is turned off, the secondary winding releases a high-voltage pulse, supplying power to the transducer. By controlling the on / off time and frequency of the switching transistor, the peak value and repetition frequency of the pulse voltage can be adjusted. The high-voltage power supply is the driving device of the vibration source system, and its parameter matching affects the quality of the excitation signal.

[0022] Indication is a method of transmitting control signals, used to exchange information and status between various components of the system. Common indication methods include level indication, pulse indication, and digital indication. Level indication uses high and low levels to represent switching states, such as a high-level trigger signal. Pulse indication uses the number of pulses to represent a count value, such as the number of excitations by the vibrator. Digital indication uses parallel or serial encoding to represent data content, such as the excitation frequency control word. Indication signals are usually generated by the control module and transmitted to the actuators through an electrical interface to achieve system synchronization and coordination. The temperature compensation value of the high-voltage pulse peak voltage is a control data to correct the temperature drift of the excitation energy. The domain orientation performance of piezoelectric ceramics is significantly affected by temperature; as the temperature rises, its electromechanical coupling coefficient decreases, and the transduction efficiency decreases. To ensure a constant excitation signal amplitude, the high-voltage pulse peak voltage needs to be dynamically adjusted to offset the temperature effect. The temperature compensation value is calculated from the ambient temperature of the system operation and the temperature characteristic curve of the piezoelectric material. It is transmitted to the high-voltage power supply in digital form by the vibrator control module, and after D / A conversion, it is superimposed on the amplitude control voltage to achieve closed-loop power control. A piezoelectric ceramic stack is a composite piezoelectric element made by stacking multiple piezoelectric ceramic sheets. The vibrational displacement of a single piezoelectric ceramic sheet is very small, typically on the order of micrometers, making it difficult to generate effective excitation. By mechanically connecting multiple ceramic sheets in series and electrically connecting them in parallel, their vibrational displacements can be accumulated, significantly increasing the excitation energy. Simultaneously, the parallel structure reduces the element's impedance, which is beneficial for matching with high-voltage power supplies. The design of the number and size of the piezoelectric ceramic stack must balance transduction efficiency and bandwidth, and is a key factor affecting the source performance. Currently, the commonly used piezoelectric ceramic materials are the PZT series, among which PZT-4 and PZT-5 varieties have high electromechanical coupling coefficients and good temperature stability, making them the preferred materials for piezoelectric ceramic stacks.

[0023] Preferably, the gravity-coupled contact source transducer includes a conductive coil and a vibrating hammer. The conductive coil is fixed on a wheeled frame, and the vibrating hammer is located at the center of the conductive coil. When a high-voltage pulse signal passes through the conductive coil, a strong magnetic field is generated in the conductive coil. Under the action of the strong magnetic field, the vibrating hammer moves at high speed and strikes the ground, generating a simulated seismic signal. The source excitation control module includes an MCU controller and a relay. The input terminal of the MCU controller is electrically connected to a trigger switch, and the output terminal of the MCU controller is electrically connected to the control terminal of the relay. The input terminal of the relay is electrically connected to the output terminal of the high-voltage power supply, and the output terminal of the relay is electrically connected to the gravity-coupled contact source transducer. After the trigger switch is closed, the high-level trigger signal generated is transmitted to the MCU controller. The MCU controller outputs a control signal to the relay. After the relay is closed, the high-voltage power supply supplies power to the gravity-coupled contact source transducer.

[0024] Furthermore, the seismic source excitation control module includes: a storage unit, a temperature acquisition unit, and a signal generation unit; the storage unit is used to store preset excitation parameters, which include the target frequency, duration, and energy of the seismic wave; the temperature acquisition unit is used to acquire temperature data obtained by an ambient temperature sensor; the signal generation unit is used to generate a first digital control signal based on the excitation parameters; and simultaneously, based on the acquired temperature data and a preset temperature compensation strategy, to generate a second digital control signal.

[0025] The preset temperature compensation strategy includes: dividing the ambient temperature range into multiple temperature intervals, each temperature interval corresponding to a preset high-voltage pulse peak voltage compensation value; determining the temperature interval to which the current temperature belongs based on the collected temperature data, and obtaining the peak voltage compensation value corresponding to the temperature interval; adding the obtained peak voltage compensation value to the reference peak voltage to obtain the compensated target peak voltage, and converting the target peak voltage into a second digital control signal; wherein, the reference peak voltage is the high-voltage pulse peak voltage of the target capability at a preset reference temperature.

[0026] By testing and statistically analyzing the relationship between the vibration amplitude of the piezoelectric ceramic stack and the peak voltage at different temperatures, peak voltage compensation values ​​for different temperature ranges are obtained. For example, each 10°C range can be considered as a separate range, such as 0-10°C, 10-20°C, and 20-30°C. The difference between the peak voltage of the high-voltage pulse required for the piezoelectric ceramic stack to output the same vibration energy within each range and the reference voltage (voltage at 20°C) is calculated and used as the compensation value for that temperature range. The signal generation unit can quickly determine and retrieve the compensation value for the corresponding range based on real-time temperature measurements. After adding it to the reference voltage, the compensated target peak voltage is obtained, which then generates a second digital control signal to control the output of the programmable high-voltage power supply, ensuring that it outputs a high-voltage pulse with a constant peak value under different temperature conditions, ultimately guaranteeing a stable simulated seismic signal output by the seismic source transducer.

[0027] Preferably, a hysteresis term is introduced into the temperature compensation formula to establish a dynamic model of the piezoelectric ceramic stack temperature and the ambient temperature. The hysteresis order and coefficients of the model are determined through a system identification method. When the ambient temperature changes, the actual temperature of the ceramic stack is predicted based on the hysteresis model, and then substituted into the compensation formula to calculate the compensation value. Temperature hysteresis compensation reduces dynamic temperature error and improves the dynamic performance of temperature compensation. An adaptive compensation strategy is adopted to adjust the coefficients of the compensation formula in real time according to the output performance of the piezoelectric ceramic stack. Specifically, a voltage sampling circuit is connected in parallel at the output terminal of the piezoelectric ceramic stack to monitor its output voltage amplitude. The sampled voltage is compared with the target amplitude to obtain the amplitude error. The error signal is fed back to the adaptive algorithm, and the compensation formula coefficients are corrected in real time through parameter estimation methods (such as LMS, RLS, etc.). Adaptive compensation can track changes in the temperature characteristics of the piezoelectric ceramic stack, automatically correct the compensation model, and ensure the long-term stability of the compensation accuracy.

[0028] Furthermore, the high-voltage power supply includes: a high-voltage pulse generation circuit and a high-voltage switch; the high-voltage pulse generation circuit has its input terminal connected to the frequency control interface and amplitude control interface of the seismic source excitation module, and receives a first digital control signal and an analog control voltage; the high-voltage pulse generation circuit generates a high-voltage pulse signal according to the frequency and number of pulses in the first digital control signal; simultaneously, it adjusts the peak voltage of the generated high-voltage pulse signal according to the amplitude of the analog control voltage; the high-voltage switch has its control terminal connected to the switch control interface of the seismic source excitation control module, its input terminal connected to the high-voltage pulse generation circuit, and its output terminal connected to a gravity-coupled contact source transducer, used to control the power supply of the high-voltage pulse signal to the gravity-coupled contact source transducer.

[0029] Furthermore, the gravity-coupled contact-type seismic source transducer includes: a piezoelectric ceramic stack, a vibration transmission rod, and a metal base plate; the piezoelectric ceramic stack has its input end connected to the output end of a high-voltage switch, used to generate mechanical vibration under the excitation of a high-voltage pulse signal; the vibration transmission rod has one end connected to the vibration output surface of the piezoelectric ceramic stack and the other end connected to the metal base plate, used to transmit the mechanical vibration generated by the piezoelectric ceramic stack to the metal base plate; the metal base plate converts the mechanical vibration of the vibration transmission rod into a simulated seismic signal, and couples the simulated seismic signal vertically downward to the ground through its direct contact surface with the ground.

[0030] Furthermore, the detector system includes multiple gravity-coupled detectors spaced apart along the circumference of the wheel frame. Each gravity-coupled detector includes at least two detector units spaced apart along the axial direction of the wheel frame. Each detector unit includes a permanent magnet, a magnetic diaphragm, and a coil. When a detector unit receives vibrations caused by a simulated seismic signal, the magnetic diaphragm moves relative to the permanent magnet, generating an induced current in the coil that is proportional to the amplitude of the simulated seismic signal. The detector unit converts the induced current into an electrical signal corresponding to the simulated seismic signal and transmits the electrical signal to the amplification circuit of the data control system for amplification.

[0031] The magnetic diaphragm is made of permanent magnet material and has a ring coil circumferentially arranged around it. When a simulated seismic signal acts on the magnetic diaphragm, it vibrates, generating an induced current in the ring coil corresponding to the simulated seismic signal. The detector unit is the basic component of the gravity-coupled detector, consisting of a permanent magnet, a magnetic diaphragm, and a coil, used to convert the simulated seismic signal into an electrical signal. When a seismic wave reaches the detector unit, the magnetic diaphragm vibrates relative to the permanent magnet under inertial force, changing the magnetic flux in the coil and inducing a current signal proportional to the vibration velocity. Through the series-parallel design of the detector units, the detector's sensitivity and bandwidth can be optimized. Combining multiple detector units allows for the synchronous acquisition of seismic waves from different azimuths and offsets, improving the system's spatial resolution and signal-to-noise ratio. The permanent magnet is a permanent magnet with a stable magnetic field, made of highly coercive ferrite or rare-earth materials. In the detector unit, the permanent magnet provides a stable magnetic bias field, serving as a reference for the vibration of the magnetic diaphragm. The magnetic field strength and magnetization direction of the permanent magnet are key parameters affecting the detector sensitivity. To avoid magnetic field interference between adjacent detector units, permanent magnets often use high-coercivity materials such as neodymium iron boron, which have high remanence density and concentrated magnetic field distribution. By optimizing the geometry and arrangement of the permanent magnets, crosstalk between detector units can be effectively reduced, improving the consistency and reliability of the detector. The magnetic diaphragm is a flexible magnetic conductor film that acts as a coupling electromechanical converter in the detector unit. Magnetic diaphragms are generally made of soft magnetic alloys with high permeability, such as permalloy and amorphous alloys. They are characterized by high permeability, low coercivity, and good magnetostriction effect. When seismic waves cause the magnetic diaphragm to vibrate, the magnetic domains inside the diaphragm shift, changing its permeability, which in turn modulates the magnetic field distribution of the permanent magnet, inducing a current signal in the coil. The material properties, thickness, and planar dimensions of the magnetic diaphragm determine the sensitivity, frequency response, and mechanical impedance of the detector unit. By optimizing the material formulation and process parameters of the magnetic diaphragm, high signal-to-noise ratio and wide bandwidth detection performance can be obtained.

[0032] Furthermore, it also includes: a trigger switch of the data control system and a gravity-coupled contact source transducer of the source system, symmetrically arranged on the same radial interface of the wheel frame and spaced apart along the axial direction of the wheel frame; when the wheel frame moves to a preset position, the trigger switch and the gravity-coupled contact source transducer simultaneously contact the ground under the gravity of the wheel frame; the trigger switch is equipped with an elastic element, when the trigger switch is compressed by the reaction force of the road surface to the elastic element to a preset threshold, the trigger switch circuit closes and outputs a high-level trigger signal to the data control system and the source system, triggering seismic wave excitation and signal acquisition; after receiving the trigger signal, the source system generates a simulated seismic signal from the gravity-coupled contact source transducer and couples it to the road base layer, the signal propagates along the road base layer and the wheel frame to a set of gravity-coupled geophones symmetrically arranged with the gravity-coupled contact source transducer; the gravity-coupled geophones symmetrically acquire the simulated seismic signal generated by the source excitation and convert it into an electrical signal to be transmitted to the data control system for synchronous control of source excitation and signal acquisition.

[0033] Preferably, the gravity-coupled detectors in a group of gravity-coupled detectors located at the same circumferential angle as the trigger switch and the gravity-coupled contact source transducer are mechanically connected by connectors to form an integrated detection unit. The trigger switch includes a housing, an elastic element, a contact, and a contact support; the bottom of the housing has an opening, one end of the elastic element is fixedly connected to the inner wall of the top of the housing, and the other end of the elastic element is fixedly connected to one end of the contact support; the other end of the contact support is fixedly connected to one end of the contact, and the other end of the contact extends to the opening of the housing; a return spring is provided between the contact support and the housing, and the two ends of the return spring are fixedly connected to the contact support and the inner wall of the housing, respectively; another contact that mates with the contact is fixedly installed on the inner wall of the housing, and the contact surfaces of both contacts are coated with conductive material; when the wheeled frame moves to a preset position, the trigger switch descends with the wheeled frame and, under the action of gravity, touches the ground. Upon contact, the contact point moves upward under the reaction force of the ground and is subjected to a preset threshold pressure. Under this pressure, the elastic element deforms, pushing the contact support and the contact point upward until the contact point contacts and remains in contact with another contact point on the inner wall of the housing, thus closing the trigger switch. After the trigger switch closes, its output terminal sends a high-level trigger signal to the control circuit of the data acquisition and control system and the source excitation control module of the source system to trigger source excitation and data acquisition. As the wheeled frame continues to move, the trigger switch detaches from the ground, and under the action of the return spring, the contact support and the contact point return to their initial position, and the trigger switch opens.

[0034] Compared to existing technologies, the advantages of this application are:

[0035] A gravity-coupled contact source transducer and detector are employed, utilizing the self-weight of the wheeled frame to generate a stable coupling force, ensuring the effective excitation and acquisition of simulated seismic signals. The source transducer uses a piezoelectric ceramic stack to generate high-frequency vibrations, which are converted into vertically downward radial vibrations coupled to the road through a vibration transmission rod and a metal base plate, resulting in high excitation efficiency and reliable coupling. The detector employs a permanent magnet-magnetic diaphragm-coil structure, utilizing the magnetoelectric conversion principle to achieve sensitive detection of simulated seismic signals.

[0036] The seismic source system introduces energy adaptive control based on ambient temperature. A temperature sensor is used to detect the current ambient temperature in real time. The seismic source excitation control module calculates the temperature drift of the piezoelectric ceramic stack based on the temperature value. The peak voltage of the high-voltage pulse is dynamically adjusted through digital control signals to compensate for the temperature characteristics of the piezoelectric ceramic stack. This ensures that the seismic source transducer maintains a stable and consistent excitation energy output, effectively eliminating the influence of ambient temperature changes on the detection signal and ensuring the reliability of the detection results.

[0037] The data control system and the seismic source system work in tandem. Trigger switches, arranged in the same radial plane of the wheeled frame, are activated by the road surface reaction force, simultaneously initiating seismic source excitation and data acquisition. This ensures strict alignment between the excitation signal and the acquisition window, avoiding detection blind spots caused by time window offsets and enabling comprehensive road scanning. Furthermore, a one-to-one source-detector synchronous triggering mode is employed, continuously acquiring data along the circumference of the wheeled frame. This provides comprehensive elastic wave response information of the roadbed, improving the detection rate of road defects and enabling precise location of affected areas.

[0038] The data control system adopts a multi-channel parallel acquisition architecture, which supports the independent operation of multiple source-detector units. It can simultaneously acquire detection data at different radial positions. With the continuous rolling of the wheeled frame, it can complete the full coverage scan of the road in both the lateral and longitudinal directions in a single survey line movement, which greatly improves the detection efficiency compared to the conventional point-by-point acquisition mode. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a road detection equipment module based on elastic waves, as shown in some embodiments of this specification.

[0040] Figure 2 This is a schematic diagram of a road detection device based on elastic waves, as shown in some embodiments of this specification;

[0041] Figure 3 This is a schematic diagram of a measurement result according to some embodiments of this specification;

[0042] Figure 4 This is a schematic diagram illustrating another measurement result according to some embodiments of this specification. Detailed Implementation

[0043] The methods and systems provided in the embodiments of this specification will now be described in detail with reference to the accompanying drawings.

[0044] Figure 1 This is a schematic diagram of a road detection equipment module based on elastic waves, as shown in some embodiments of this specification. The elastic wave-based road detection equipment includes: a data control system, a geophone system, a seismic source system, and a wheeled frame; the data control system is used to control the excitation of the seismic source system, acquire and record the simulated seismic signals received by the geophone system and the spatial coordinate data of the geophone system; the geophone system includes multiple gravity-coupled geophones spaced at intervals along the circumference of the wheeled frame, used to receive the simulated seismic signals generated by the seismic source system and coupled to the ground, and convert the simulated seismic signals into electrical signals and transmit them to the data control system; the seismic source system, under the control of the data control system, generates simulated seismic signals and couples them to the ground; the wheeled frame is used to mount the geophone system and the seismic source system, driving the seismic source system and the geophone system to acquire data on the structure beneath the road during movement.

[0045] Figure 2 This is a schematic diagram of a road detection equipment based on elastic waves, as shown in some embodiments of this specification. The data control system is one of the core components of the rapid road detection equipment, mainly composed of a trigger switch, a GPS positioning system, an amplification circuit, and a control circuit. Its specific implementation is as follows: The trigger switch is an electromechanical switch with an elastic element, arranged symmetrically with the seismic source transducer on a wheeled frame. When the wheeled frame drives the trigger switch to a preset acquisition position, the elastic element deforms under the pressure of the road surface reaction force, triggering the switch to close and generating a high-level trigger signal with a duration of 10–50 ms. This signal is transmitted in two ways: one path to the seismic source system to activate the transducer; the other path to the control circuit to initiate data acquisition and coordinate association.

[0046] GPS Positioning System: A differential GPS receiver is used and mounted on top of the wheeled frame. The receiver calculates the equipment's current location's three-dimensional coordinates (latitude, longitude, elevation, etc.) by measuring the pseudorange of at least four GPS satellites, achieving a positioning accuracy better than 0.5m. The coordinate data is transmitted to the control circuit via an RS232 serial interface and updated every 0.1s. Amplification Circuit: A multi-stage cascaded instrumentation amplifier circuit is connected to the output of the gravity-coupled geophone. When the geophone senses a weak simulated seismic signal reflected from the roadbed, the amplifier circuit amplifies it to within a 180dB range.

[0047] Control Circuit: Based on an ARM Cortex-M7 series microcontroller, the control circuit integrates analog-to-digital conversion, digital signal processing, data storage, and communication functions. Upon receiving a high-level trigger signal from the trigger switch, the control circuit initiates analog-to-digital conversion, digitizing the amplified analog seismic signal at a sampling rate of 200kHz and a resolution of 16 bits, continuously acquiring 2048 data points. Simultaneously, the control circuit obtains current spatial coordinate data from the GPS positioning system and timestamps it with the digitized seismic waveform data, forming a seismic gather with a unique coordinate identifier. After acquisition, the control circuit uses its built-in DSP unit to preprocess the seismic gather, including denoising, filtering, and amplitude recovery, improving the signal-to-noise ratio and highlighting seismic event characteristics. The preprocessed seismic gather is transferred to an external Flash memory via DMA, with each gather containing approximately 4kB of data. When the storage space reaches a threshold (e.g., 1GB), the control circuit automatically uploads the data to the roadside unit and marks the storage space as overwhelmable, enabling cyclic data acquisition and networked transmission.

[0048] When the wheeled frame drives the trigger switch and the seismic source transducer to the preset acquisition position, both simultaneously come into contact with the road surface under the action of gravity. When the trigger switch is compressed by the reaction force of the road surface to the elastic element and reaches the preset threshold, the trigger switch circuit closes and outputs a high-level trigger signal, synchronously starting the seismic wave excitation and signal acquisition.

[0049] The seismic source system is a key component of rapid road inspection equipment. Its function is to generate high-frequency mechanical vibrations to excite the road base layer, providing energy input for defect detection. To overcome the influence of ambient temperature changes on the excitation performance of piezoelectric ceramics, this seismic source system adopts a temperature-compensated energy adaptive control strategy, the specific implementation of which is as follows: The seismic source excitation control module integrates a digital temperature sensor. Upon receiving a high-level trigger signal from the trigger switch, the temperature sensor collects the real-time temperature of the environment where the seismic source transducer is located and transmits the digitized temperature data to the seismic source excitation control module via an I2C bus. The temperature sampling range is -40 to 85℃, the sampling accuracy is better than ±0.5℃, and the sampling period is 1 second.

[0050] The source excitation control module has a built-in Flash memory that pre-stores the temperature characteristic curves and temperature compensation strategies of the piezoelectric ceramic stack. The temperature characteristic curves describe the dependence of parameters such as the electromechanical coupling coefficient and quality factor of the piezoelectric ceramic stack on temperature. Based on this, the peak voltage of the high-voltage pulse required to maintain an 80dB sound intensity level output at different temperatures can be calculated.

[0051] The temperature compensation strategy divides the ambient temperature range of -20 to 50°C into seven intervals: (-20, -10], (-10, 0], (0, 10], (10, 20], (20, 30], (30, 40], (40, 50). Each interval corresponds to an empirically determined peak voltage compensation value: 200V, 150V, 100V, 50V, 0V, -50V, and -100V. The physical meaning of the compensation value is: within this temperature range, to compensate for the reduction in sound intensity level caused by changes in the temperature characteristics of the piezoelectric ceramic stack, the voltage value that needs to be added or subtracted from the reference peak voltage.

[0052] Upon receiving temperature data, the seismic source excitation control module determines which preset temperature range it belongs to, extracts the corresponding peak voltage compensation value for that range, and adds it to a reference peak voltage of 1500V (when the compensation value is negative, it is equivalent to subtracting its absolute value) to obtain the temperature-compensated target peak voltage. Taking an actual collected temperature of 25℃ as an example, it falls within the range (20, 30], with a corresponding compensation value of 0V. The target peak voltage = 1500V + 0V = 1500V.

[0053] The seismic source excitation control module generates two digital control signals: the first is a frequency control signal, which instructs the high-voltage pulse generation circuit to output 20 cycles of pulses at a repetition frequency of 1000Hz. The first control signal is 40-bit TTL level data, with the encoding rule of "20 1000Hz pulses + 20 low-level intervals"; the second is an amplitude control signal, which converts the target peak voltage into a 16-bit unsigned integer. The second control signal is 16-bit TTL level data, with the encoding rule of "065535".

[0054] The frequency control signal is directly input to the trigger interface of the high-voltage pulse generation circuit, while the amplitude control signal is converted into a 0-5V analog voltage via a 16-bit digital-to-analog converter chip (DAC8831) and input to the peak modulation interface of the high-voltage pulse generation circuit. Based on the first digital control signal received from the trigger interface, the high-voltage pulse generation circuit generates a 1000Hz, 20ms high-voltage pulse sequence according to the specified frequency and number, through a high-voltage transformer and a high-voltage switch. Simultaneously, based on the analog voltage from the peak modulation interface, the peak voltage of the pulse sequence is adjusted from the rated 1500V to the target value to achieve temperature compensation.

[0055] After being switched by a high-voltage switch, the high-voltage pulse sequence is finally applied to the piezoelectric ceramic stack inside the seismic source transducer. Under this temperature compensation strategy, the peak voltage experienced by the piezoelectric ceramic stack is basically consistent with the operating voltage at the reference temperature, and the output sound intensity level remains at around 80dB. Problems such as temperature-induced sensitivity drift and decreased electromechanical conversion efficiency are effectively mitigated. The seismic source system acquires ambient temperature information in real time through an integrated temperature sensor and dynamically adjusts the peak voltage parameters of the high-voltage pulse according to the preset temperature compensation strategy. This stabilizes the performance of the piezoelectric ceramic stack as an excitation element, ensuring the consistency of the excitation energy of the road rapid detection equipment under different climatic conditions, and providing a reliable guarantee for the quantitative interpretation of subsequent damage information.

[0056] The high-voltage pulse generation circuit is the execution unit of the seismic source system. Based on the digital control signals provided by the seismic source excitation control module, it synthesizes a high-voltage pulse sequence with a specified frequency and amplitude. After being switched by a high-voltage switch, it drives the piezoelectric ceramic stack to generate mechanical vibration. Its specific implementation is as follows: The high-voltage pulse generation circuit mainly consists of a step-up transformer, a high-voltage rectifier bridge, an energy storage capacitor, and an IGBT switch. The primary winding of the step-up transformer is connected to 220V AC mains power, and the secondary winding outputs high-voltage pulses from 0 to 5000V. The high-voltage rectifier bridge converts the AC high-voltage pulses to DC and charges the 100μF / 5kV energy storage capacitor. The IGBT switch is connected in series between the energy storage capacitor and the seismic source transducer, serving to turn off and on the high-voltage pulses. The input terminal of the high-voltage pulse generation circuit receives two digital control signals from the seismic source excitation control module: the first is a frequency control signal, and the second is an amplitude control signal. The frequency control signal is a 40-bit TTL level waveform data, encoded as “20 high-level pulses of 1000Hz + 20 low-level intervals”, used to trigger the IGBT switching transistor to turn on and off; the amplitude control signal is a 16-bit TTL level data, encoded as “05000V”, which is converted into an analog voltage of 0-5V by the DAC8831 digital-to-analog converter chip, used to adjust the output voltage of the secondary winding of the step-up transformer.

[0057] The control logic of the high-voltage pulse generation circuit is as follows: The gate of the IGBT switch is connected to an optocoupler drive circuit, which is triggered by a frequency control signal. When the frequency control signal is high, the optocoupler is turned on, and its gate voltage is pulled up to 15V, turning on the IGBT switch. The high-voltage pulse on the energy storage capacitor is applied to the transducer through the IGBT switch. When the frequency control signal is low, the optocoupler is turned off, and its gate voltage is pulled down to 0V, turning off the IGBT switch. The transducer is then disconnected from the energy storage capacitor. This cycle repeats 20 times, generating 20 high-voltage pulses on the transducer.

[0058] During IGBT switching, the energy storage capacitor discharges to the transducer, but due to the very short pulse duration (1ms), the voltage drop across the energy storage capacitor is not significant. During IGBT switching, the high-voltage rectifier bridge charges the energy storage capacitor, restoring it to its peak voltage before the next IGBT switching cycle. A thyristor voltage regulator module is connected in parallel across the primary winding of the step-up transformer, and its control terminal is connected to the amplitude control interface. The amplitude control interface outputs within the range of 0-5000V.

[0059] By combining the effects of frequency control and amplitude control, the high-voltage pulse generation circuit can generate a pulse sequence of 20 high-voltage pulses at a repetition frequency of 1000Hz, with the peak voltage of each pulse equal to the target peak voltage. When the target peak voltage is 1500V, the parameters of the pulse sequence are: peak voltage 1500V, number of pulses 20, repetition frequency 1000Hz, and total duration 20ms.

[0060] After being switched by an IGBT switch, the output of the high-voltage pulse sequence is directly connected to the insulating terminals of the vibrating source transducer base. The vibrating source transducer uses a piezoelectric ceramic stack with a diameter of 50 mm and a height of 30 mm as the excitation element. Its equivalent capacitance is 20 nF, which is negligible compared to the 100 μF energy storage capacitor. Therefore, it can be equivalent to applying the high-voltage pulse sequence directly to both ends of the piezoelectric ceramic stack. Under this excitation, the piezoelectric ceramic stack generates a mechanical vibration with an amplitude of 210 kHz along the axial direction, which is transmitted to the metal base plate through the vibration transmission rod at the front end.

[0061] The metal base plate is made of 304 stainless steel with a diameter of 150mm and a thickness of 10mm, and is connected to the vibration transmission rod via threads. The base plate is driven by the vibration transmission rod to perform axial reciprocating motion with an amplitude of 2-5μm. Because the diameter of the base plate is much larger than its thickness, the radial component of the axial vibration within the base plate is much larger than the axial component, causing the base plate to exhibit vibration characteristics similar to a planar sound source, converting the axial vibration into vertically downward out-of-plane vibration.

[0062] When the detection equipment is in operation, the base plate is in close contact with the road surface. Under the combined action of its own weight and the gravity of the wheeled frame, it radiates downwards in the form of seismic waves with a frequency band of 100-2000 Hz and an acoustic intensity of 0.1–1 MPa, exciting the road base layer to generate a dynamic response and forming seismic reflection waves of the road structure. These reflected waves carry information about the spatial distribution of the road's internal structure and return to the road surface along their propagation path, where they are received by gravity-coupled geophones positioned symmetrically to the source transducer. The geophones pick up the road surface vibration velocity caused by the reflected waves and convert it into a current signal output proportional to the vibration velocity, thus realizing the acquisition of simulated seismic signals. The high-voltage pulse generation circuit controls the IGBT switching transistor through an optocoupler drive circuit, converting the digitized frequency control signal into the time-domain parameters of the high-voltage pulse sequence. The secondary winding voltage of the step-up transformer is adjusted via a thyristor voltage regulation module, converting the digitized amplitude control signal into the peak parameters of the high-voltage pulse. The switching on and off processes of the high-voltage switch change the pulse sequence, driving the piezoelectric ceramic stack-vibration transmission rod-metal base plate to form a machine-sound conversion unit. Under specified repetition frequency, pulse count, and peak voltage conditions, it generates out-of-plane vibrations with a specified duration and intensity, achieving temperature-adaptive vibration source excitation. The gravity coupling mechanism ensures the efficient conversion of excitation energy to the road surface, which is crucial for improving detection efficiency and depth.

[0063] The seismic source transducer is an actuator that converts high-voltage electrical pulse signals into mechanical vibrations. These vibrations are coupled to the road surface via the base plate, propagate within the base layer, and are received by a detector, converting them into current signals corresponding to the characteristics of seismic signals. The specific implementation of this process is as follows: The piezoelectric ceramic stack consists of 10 PZT-8 piezoelectric ceramic sheets, each 50mm in diameter and 3mm thick, assembled with conductive adhesive. Its equivalent capacitance is 20nF. When a high-voltage pulse sequence is applied to both ends of the piezoelectric ceramic stack, under the inverse piezoelectric effect, each ceramic sheet undergoes axial deformation along the polarization direction. The cumulative deformation of the 10 ceramic sheets causes the piezoelectric ceramic stack to produce an axial stretching vibration of approximately 1nm / V.

[0064] When the high-voltage pulse sequence parameters are 1500V peak, 1000Hz repetition, and 20 pulses, the piezoelectric ceramic stack generates a mechanical vibration with an amplitude of 1.5μm and a frequency band of 30kHz in the axial direction, lasting 20ms. This mechanical vibration is transmitted to the metal base plate through a vibration transmission rod at the front end. The vibration transmission rod is made of stainless steel, with a diameter of 10mm and a length of 100mm, and serves to match impedance and transfer energy. The metal base plate is made of 304 stainless steel with a diameter of 150mm and a thickness of 10mm, and its vibration mode is axial vibration. Because the diameter of the base plate is much larger than its thickness, its vibration is mainly radial and perpendicular to the road surface. When the detection equipment is working, the base plate is pressed against the road surface by its own weight and the gravity of the wheeled frame, forming a coupling pressure of approximately 200kPa. Under these conditions, the vibration energy conversion efficiency between the base plate and the road surface can reach over 80%.

[0065] The vibration of the roadbed slab, similar to that of a hammer excitation, converts mechanical vibration with an amplitude of 1.5 μm, a frequency band of 30 kHz, and a duration of 20 ms into seismic waves incident on the road base layer. The waveform parameters are: dominant frequency 500 Hz, frequency band 100 Hz-2 kHz, pulse width 5 ms, and sound pressure level 120 dB. These seismic waves propagate within the road base layer at speeds of 1000–2000 m / s, and are reflected upon encountering structural interfaces. The reflected waves carry information about the internal road structure. After returning to the road surface, the reflected waves excite longitudinal and lateral vibrations in the area adjacent to the seismic source. The longitudinal vibrations are mainly caused by surface disturbances and have a higher frequency; the lateral vibrations are mainly caused by base layer disturbances and have a relatively lower frequency. These two vibration components superimpose in space and time, forming a complex road vibration field.

[0066] The gravity-coupled detector is fixed to a wheeled frame and pressed against the road surface by gravity to pick up the road vibration velocity signal caused by reflected waves. Each detector unit is 50mm in diameter and 30mm in height, with 1000 coil turns and a coil resistance of 100Ω. When the detector diaphragm velocity is 1mm / s, the coil induced current amplitude is 0.1mA. The magnetic diaphragm is made of 0.2mm thick iron-nickel alloy, and the permanent magnet is made of neodymium iron boron, providing a magnetic field strength of 1T. When the detector receives road vibration, the magnetic diaphragm reciprocates in the permanent magnet's magnetic field, inducing a current signal in the coil that is proportional to the diaphragm's velocity. Because the mass of the magnetic diaphragm is much smaller than that of the detector housing, vibration signals can be picked up over a wide frequency band.

[0067] Considering that road surface vibration is a complex vector field, a single geophone cannot accurately characterize its vibration properties. Therefore, each gravity-coupled geophone integrates two geophone units spaced 50 cm apart along the axial direction of the wheel frame. The two geophone units synchronously pick up the vibration signal of the reflected wave, and the apparent velocity and incident angle of the reflected wave along the propagation path can be calculated through cross-correlation calculations.

[0068] After amplifying and digitizing the induced current signal from the gravity-coupled geophone, a digital seismic signal corresponding to the vibration characteristics of the road surface reflected waves can be obtained. Envelope extraction and spectral analysis of this signal yield seismic attribute parameters related to the road base structure characteristics, enabling imaging interpretation of the road's internal structure. The source transducer converts high-voltage pulses into mechanical vibrations via a piezoelectric ceramic stack. Through mechanical amplification and impedance matching by the vibration transmission rod and base plate, broadband seismic waves are excited in the road base, making it the core unit for simulating seismic signal generation. The gravity-coupled geophone, through a magneto-mechanical-electric conversion mechanism, achieves distortion-free pickup and digitization of the road surface reflected wave vibration signal, crucial for extracting road structure information. Together, they achieve efficient acquisition of road structure mechanical parameters through an "active excitation – road response – passive reception" approach, forming the core functional unit of rapid non-destructive testing equipment. The wheeled frame, through a gravity mechanism, ensures tight coupling between the two components and the road surface, improving excitation efficiency and receiving sensitivity, a key factor in guaranteeing testing performance.

[0069] The analog seismic signal output by the detector unit has a small amplitude and needs to be amplified and digitized to meet subsequent processing requirements. The amplification circuit employs dynamic range matching technology to automatically adjust the amplification factor based on signal characteristics, avoiding signal distortion. The digital signal processing unit, implemented through software, performs signal conditioning and feature extraction, and is the core of signal enhancement and parameter inversion. The specific implementation scheme is as follows: The detector unit receives the road vibration velocity generated by the seismic signal, induces a current signal with an amplitude of 0.0110kHz in the coil through magneto-electric conversion, and transmits it to the data control system via a shielded cable. The front end of the data control system is an 8-channel current amplifier with a bandwidth of 1MHz, responsible for amplifying the 0.0110V voltage signal by approximately 50 times. The voltage signal passes through an RC passive low-pass filter to remove high-frequency interference above 500kHz before being fed into a secondary amplification circuit with programmable gain.

[0070] The secondary amplifier circuit uses a VCA810 programmable amplifier, providing an amplification range of -40dB to +40dB with a gain step of 1dB. Its control terminal is connected to an 8-bit DAC, generated by FPGA logic, for digital adjustment of the amplification factor. The amplifier output is connected to a 10-bit AD sample-and-hold circuit, digitizing the signal at a 10MHz sampling rate. The FPGA integrates a signal amplification control module, employing an adaptive gain control strategy. It monitors the AD converter output data in real time, evaluates the signal dynamic range, and provides a gain control word, which is converted into an analog voltage by the DAC and fed back to the gain control terminal of the VCA810 amplifier. This control process is completed within 1μs, enabling tracking of instantaneous amplitude changes in the seismic signal.

[0071] The adaptive gain control strategy is based on the principle of signal dynamic range matching. It uses the peak value of the digital signal to represent its amplitude. When the peak value is less than 1 / 8 of the full-scale AD converter, the amplification factor is increased by 6dB; when the peak value is greater than 1 / 2 of the full-scale AD converter, the amplification factor is decreased by 6dB. The control objective is to stabilize the signal peak value at 1 / 4512 LSB of the full-scale AD converter to achieve dynamic range matching.

[0072] When the signal peak value is less than 32 LSB (approximately 12.5 mV), the amplification factor is fixed at +40 dB, and the FPGA prevents the amplification factor from increasing further. This threshold level is 10 times higher than the system noise floor, preventing noise from being amplified to full scale by the AD converter and masking weak signals. When the signal peak value is greater than 896 LSB (approximately 3.5 V), the control logic fixes the amplification factor at -20 dB to prevent hardware damage to the amplifier output due to excessively large signals.

[0073] The FPGA packages the AD data into frames and uploads them to the industrial computer via a USB 2.0 interface, where the host computer software performs subsequent processing. The host computer software, developed based on LabVIEW, integrates virtual instruments such as digital filtering, envelope extraction, and spectrum analysis. The digital filtering uses a 6th-order Butterworth filter with a passband range of 20Hz to 5kHz, primarily for eliminating road background noise.

[0074] For the filtered digital signal, the host computer extracts its amplitude envelope to characterize the change of vibration energy over time. The extraction method is as follows: take the absolute value of the signal, and then smooth it using a 100-point moving average filter to obtain the signal envelope. Peak detection is performed on the signal envelope, and the amplitude, time, and index of the local maxima are used as candidate attribute parameters. The host computer performs a 1024-point FFT transform on the digital signal to obtain the signal spectrum. Three peaks with the highest energy are selected from the spectrum, and their amplitude, frequency, and index are extracted as frequency domain attribute parameters. Combining the time domain and frequency domain parameters, a total of 6 feature quantities are obtained as the digital representation of the simulated seismic signal.

[0075] The feature values ​​obtained from each road detection unit are uploaded to the data processing and imaging system to establish a BP neural network mapping relationship between road structural parameters and seismic signal feature values. The network is then trained with a large amount of field data, which enables the inversion from seismic signals to road internal structural parameters.

[0076] The amplifier circuit, employing a "primary amplification – programmable amplification – adaptive gain control" technical scheme, achieves low-noise, wide dynamic range, and low-distortion analog amplification of seismic signals, meeting the amplitude requirements of AD sampling. The digital signal processing unit, using software-defined methods, flexibly implements filtering, feature extraction, and other processing functions. Through collaboration with the data processing system, it establishes a mapping relationship between seismic signals and road structure parameters. The combination of these two technologies transforms the weak analog signal output from the detector unit into a digital result reflecting the internal structure of the road, a key technology for achieving rapid and high-precision road detection.

[0077] The high-voltage power supply is the power source that excites the seismic source to generate mechanical vibrations, and its performance directly determines the waveform characteristics of the excitation signal. The high-voltage switch modulates the pulse power and is the actuator controlling the excitation energy and timing. Together, they can adjust the amplitude, frequency, and duration of the seismic signal over a wide range to meet the detection needs of different road materials and structures. The specific implementation scheme is as follows: The high-voltage pulse generation circuit consists of a step-up transformer and a half-bridge circuit. The primary winding of the transformer is connected to a 300V DC bus, and the secondary winding outputs a continuously adjustable 0-100kHz frequency. When the half-bridge circuit switches, the secondary winding induces a high-voltage pulse with an amplitude proportional to the switch duty cycle.

[0078] The control terminals of the high-voltage pulse generation circuit include a 4-bit digital control terminal and a 1-channel analog control terminal. The digital control terminal is generated by an FPGA, outputting a duty cycle code, which is converted to a 15V drive level by an isolation drive circuit to control the conduction time of the half-bridge circuit, thereby adjusting the pulse frequency and number of pulses. The analog control terminal comes from a 12-bit DAC, generating a 012V feedback voltage to control the primary winding current of the step-up transformer, thereby adjusting the amplitude of the secondary high-voltage pulse.

[0079] The high-voltage switch uses a fast power relay with a maximum operating voltage of 2.5kV, a maximum current of 20A, and a switching time of 5ms. Its coil control voltage is 24V, and its drive power is 10W, directly compatible with the FPGA's general-purpose I / O ports. The normally closed terminal of the relay is connected to the high-voltage pulse generation circuit, and the normally open terminal is connected to the vibration source transducer. During operation, the FPGA first sends a switch closing control signal, then starts the half-bridge circuit to load the high-voltage pulse signal onto the vibration source transducer.

[0080] The seismic source excitation control module runs a dedicated control program that automatically generates a high-voltage power supply control strategy based on the excitation parameters set by the user. Specifically, this includes: obtaining the corresponding DAC setting value from a table based on the excitation amplitude, sending the digital signal to the DAC via the SPI interface to generate an analog control voltage; calculating the switching cycle and number of times of the half-bridge circuit based on the excitation frequency and number of times, sending the duty cycle code to the FPGA via the GPIO port; and controlling the activation and deactivation of the high-voltage switch according to the excitation timing, defining the start and end of the pulse sequence.

[0081] To improve data throughput, the detection unit first packages the sampled data within the FPGA, and then transmits it to the data control system in frames via a USB 2.0 interface. The host computer software receives the raw data frames, performs frame de-framing, attribute extraction, and data organization, and forwards them to the data storage unit via UDP protocol. Simultaneously, the host computer has data playback and query functions, facilitating user analysis of historical data.

[0082] The data storage unit uses a 256GB solid-state drive (SSD), capable of storing detection data from 10,000km of roads. The SSD connects to an embedded industrial computer via a SATA interface. The host computer writes the detection data to a designated directory on the SSD, with each data file corresponding to a 1km road segment. When storage space is insufficient, the host computer automatically deletes the oldest data file, prioritizing the storage of the latest data. The wireless communication module includes 4G and WiFi communication. The 4G module uses LTE Cat.4 technology, with a theoretical bandwidth of 150Mbps and a transmission latency of less than 50ms. Every minute, the host computer automatically packages the latest 10 data files and uploads them to the roadside unit via the 4G network, checking for successful uploads. The WiFi module uses the 802.11n protocol, supports 2T2RMIMO, and has a transmission bandwidth of up to 300Mbps. When a vehicle is within 50m of the roadside unit, it automatically switches to WiFi communication to improve data upload speed. The roadside units are deployed along the road at 5km intervals. The hardware platform uses a multi-core industrial computer with a 2.5GHz clock speed, 8GB of memory, and four GPU accelerator cards. The operating system uses a real-time enhanced Linux, which can respond to external control commands within 100ms. The roadside unit is connected to the metropolitan area network via fiber optic cable with a transmission bandwidth of 10Gbps, receiving data uploaded by all detected vehicles and aggregating it to the central node.

[0083] Figure 3 This is a schematic diagram of a measurement result according to some embodiments of this specification; Figure 4 This is a schematic diagram of another measurement result according to some embodiments of this specification. The horizontal axis represents the acquired seismic trace number, and the vertical axis represents time. The waveform is a seismic emission map of a certain location. The polarity and strength of the amplitude are related to the wave impedance of the upper interface of the underground strata. Figure 3 and Figure 4 This is a measurement result diagram of newly buried pipes in a building. It can be seen that the energy is reduced in the looser areas. Figure 3 , Figure 4As can be seen, the energy of the reflected waves is significantly reduced at certain locations, manifesting as localized dark or low-brightness areas in the image. These areas of reduced energy often correspond to locations with loose soil around the pipeline. Loose soil causes seismic waves to experience stronger attenuation and scattering during propagation, resulting in reduced energy reflected back to the ground. Conversely, in locations with dense soil, the reflected energy is relatively stronger. By comparing and analyzing the energy differences in different parts of the image, the compaction level of the soil around the pipeline can be qualitatively determined. The roadside unit runs road defect identification and road condition assessment software, employing deep learning algorithms to classify and perform regression analysis on the detection data. The defect identification software can identify 10 types of defects, including pavement cracks, ruts, and pumping, with an accuracy rate of over 95%. The road condition assessment software can determine five indicators, including subgrade compaction and slab integrity, and quantitatively provide a road condition health index. When defects or abnormal road conditions are detected, the roadside unit automatically sends an alarm to the maintenance decision-making system. The wheeled frame is made of fiberglass, with a diameter of 50cm and a width of 30cm, and is equipped with four water-filled rubber wheels. The frame is connected to the towing vehicle via a suspension system, maintaining a constant pressure of 100 kgf on the road surface. When encountering potholes smaller than 10 cm, the suspension system can lift the frame, clear the obstacle, and then automatically lower it, ensuring the continuity of the inspection process. The frame rolls at a speed of 5 km / h, and excitation and sampling are performed every 2 m, equivalent to scanning the road surface at a sampling rate of 2.5 m / s.

Claims

1. A road detection device based on elastic waves, comprising: Data control system, detector system, seismic source system, and wheeled frame; The data control system is used to control the excitation of the seismic source system, acquire and record the simulated seismic signals received by the geophone system and the spatial coordinate data of the geophone system; The detector system includes multiple gravity-coupled detectors spaced apart along the circumference of the wheel frame, used to receive simulated seismic signals generated by the source system and coupled to the ground, and to convert the simulated seismic signals into electrical signals and transmit them to the data control system. The seismic source system, under the control of the data control system, generates simulated seismic signals and couples these signals to the ground. A wheeled frame is used to mount the geophone system and the seismic source system, and to drive the seismic source system and the geophone system to collect data on the structure under the road during the movement. The trigger switch of the data control system and the contact source transducer of the gravity coupling of the source system are symmetrically arranged on the same radial interface of the wheel frame and spaced apart along the axial direction of the wheel frame. When the wheeled frame moves to the preset position, it triggers the switch and the gravity-coupled contact source transducer, which simultaneously comes into contact with the ground under the gravity of the wheeled frame. The trigger switch is equipped with an elastic element. When the trigger switch is subjected to the reaction force of the road surface and the elastic element is squeezed to a preset threshold, the trigger switch circuit closes and outputs a high-level trigger signal to the data control system and the source system to trigger seismic wave excitation and signal acquisition. After receiving the trigger signal, the source system generates a simulated seismic signal through a gravity-coupled contact source transducer and couples it to the road base. The signal propagates along the road base and the wheel frame to a set of gravity-coupled detectors symmetrically arranged with the gravity-coupled contact source transducer. Gravity-coupled geophones symmetrically acquire simulated seismic signals generated by the seismic source and convert them into electrical signals, which are then transmitted to the data control system for synchronous control of the seismic source excitation and signal acquisition.

2. The road detection equipment based on elastic waves according to claim 1, characterized in that: The data control system includes: a trigger switch, a GPS positioning system, an amplifier circuit, and a control circuit; The trigger switch is used to generate a high-level trigger signal to trigger the excitation of the source system and data acquisition, and to transmit the high-level trigger signal to the source system and control circuit. The GPS positioning system is used to acquire the spatial coordinate data of the gravity coupling detector and transmit the acquired planar spatial coordinate data to the control circuit. The amplifier circuit is used to amplify the simulated seismic signal acquired by the gravity-coupled detector and transmit the amplified seismic signal to the control circuit. The control circuit, upon receiving a high-level trigger signal, acquires spatial coordinate data and amplified simulated seismic signals, and correlates them to obtain seismic waveform data with spatial coordinates.

3. The road detection equipment based on elastic waves according to claim 2, characterized in that: The amplifier circuit amplifies the simulated seismic signal, including: The collected simulated seismic signals are converted into electrical signals and transmitted to the amplification circuit; The electrical signal is rectified and filtered to obtain a DC signal that reflects the change in the amplitude of the electrical signal; The DC signal is compared with a preset amplitude threshold voltage to determine whether the current electrical signal amplitude is within the preset signal dynamic range, thus obtaining the electrical signal amplitude detection result. Based on the amplitude detection results of the electrical signal, the electrical signal is amplified according to the preset amplification factor control strategy; The amplified electrical signal is converted into a digital signal, which is then used as an amplified simulated seismic signal.

4. The road detection equipment based on elastic waves according to claim 3, characterized in that: Based on the amplitude detection results of the electrical signal, the electrical signal is amplified according to a preset amplification factor control strategy, including: Multiple signal amplitude thresholds are preset, and these thresholds are divided into different signal amplitude ranges. The current electrical signal amplitude is compared with various amplitude thresholds to determine the amplitude range to which the current electrical signal belongs, and the corresponding amplification factor is selected from the preset amplification factor control strategy. The electrical signal is amplified using a selected amplification factor; Determine whether the amplitude of the amplified electrical signal exceeds the preset upper limit threshold for signal amplitude; If the upper limit threshold is exceeded, the selected amplification factor is reduced, and the electrical signal is amplified using the reduced amplification factor until the amplitude of the amplified electrical signal is less than the preset upper limit threshold of the signal amplitude, thus obtaining an amplified electrical signal with limited amplitude, which is used as the amplified electrical signal.

5. The road detection equipment based on elastic waves according to claim 2, characterized in that: The seismic source system includes: a gravity-coupled contact source transducer, a seismic source excitation control module, and a high-voltage power supply; The source excitation control module is used to receive the high-level trigger signal from the trigger switch and generate the first digital control signal and the second digital control signal according to the preset excitation parameters. The first digital control signal is used to indicate the number and frequency of the seismic source excitation, and is input from the frequency control interface of the high-voltage power supply by the seismic source excitation control module. The second digital control signal is used to indicate the temperature compensation value of the peak voltage of the high-voltage pulse. It is input to the amplitude control interface of the high-voltage power supply after being converted from digital to analog by the source excitation control module. The high-voltage power supply, based on the first digital control signal obtained from the frequency control interface, supplies power to the gravity-coupled contact source transducer according to the indicated frequency and number of cycles via a high-voltage switch. The high-voltage power supply adjusts the peak voltage of the high-voltage pulse signal output to the gravity-coupled contact source transducer based on the analog control voltage obtained from the amplitude control interface. The gravity-coupled contact source transducer uses a piezoelectric ceramic stack as the excitation element. Under the excitation of a high-voltage pulse signal, it generates mechanical vibration. The mechanical vibration is transmitted to the base plate through a vibration transmission rod, generating a simulated seismic signal. The base plate then couples the simulated seismic signal to the ground.

6. The road detection equipment based on elastic waves according to claim 5, characterized in that: The seismic source excitation control module includes: Storage unit, temperature acquisition unit, and signal generation unit; The storage unit is used to store preset excitation parameters, which include the target frequency, duration, and energy of the seismic wave. Temperature acquisition unit, used to acquire temperature data obtained by ambient temperature sensor; The signal generation unit is used to generate a first digital control signal based on the excitation parameters; at the same time, it generates a second digital control signal based on the collected temperature data and a preset temperature compensation strategy. The preset temperature compensation strategies include: The ambient temperature range is divided into multiple temperature zones, and each temperature zone corresponds to a preset high-voltage pulse peak voltage compensation value. Based on the collected temperature data, determine the temperature range to which the current temperature belongs, and obtain the peak voltage compensation value corresponding to the temperature range; The acquired peak voltage compensation value is added to the reference peak voltage to obtain the compensated target peak voltage, and the target peak voltage is converted into a second digital control signal; wherein, the reference peak voltage is the high-voltage pulse peak voltage of the target capability at a preset reference temperature.

7. The road detection equipment based on elastic waves according to claim 6, characterized in that: High-voltage power supply, including: high-voltage pulse generation circuit and high-voltage switch; The high-voltage pulse generation circuit has its input terminal connected to the frequency control interface and amplitude control interface of the vibration source excitation module, and receives the first digital control signal and analog control voltage. The high-voltage pulse generation circuit generates a high-voltage pulse signal based on the frequency and number of pulses in the first digital control signal; at the same time, it adjusts the peak voltage of the generated high-voltage pulse signal according to the amplitude of the analog control voltage. The high-voltage switch has its control terminal connected to the switch control interface of the seismic source excitation control module, its input terminal connected to the high-voltage pulse generation circuit, and its output terminal connected to the gravity-coupled contact source transducer. It is used to control the power supply of the gravity-coupled contact source transducer by the high-voltage pulse signal.

8. The road detection equipment based on elastic waves according to claim 7, characterized in that: Gravity-coupled contact source transducer includes: piezoelectric ceramic stack, vibration transmission rod and metal base plate; The piezoelectric ceramic stack has its input end connected to the output end of a high-voltage switch, and is used to generate mechanical vibration under the excitation of a high-voltage pulse signal. The vibration transmission rod is connected at one end to the vibration output surface of the piezoelectric ceramic stack and at the other end to the metal base plate. It is used to transmit the mechanical vibration generated by the piezoelectric ceramic stack to the metal base plate. The metal base plate converts the mechanical vibration of the vibration transmission rod into a simulated seismic signal, which is then coupled vertically downwards to the ground through contact with the ground.

9. The road detection equipment based on elastic waves according to claim 1, characterized in that: The detector system comprises multiple gravity-coupled detectors spaced apart along the circumference of the wheel frame, including: Each gravity-coupled detector comprises at least two detector units spaced apart along the axial direction of the wheel frame, and each detector unit comprises: a permanent magnet, a magnetic diaphragm, and a coil; When the detector unit receives vibrations caused by simulated seismic signals, the magnetic diaphragm moves relative to the permanent magnet, generating an induced current in the coil that is proportional to the amplitude of the simulated seismic signal. The detector unit converts the induced current into an electrical signal corresponding to the simulated seismic signal, and then transmits the electrical signal to the amplification circuit of the data control system for amplification.

Images